Ultra High Frequency Band Research Articles

Multipath Effect Analysis of Sea Surface in Maritime Satellite Communications

Ultra High Frequency (UHF) band is increasingly widely used in military maritime satellite communications due to its good communication performance. When the electromagnetic wave reaches the sea surface, it is reflected. The reflected wave and direct wave enter the receiver in the form of a superimposed vector, which will inevitably produces multipath fading at the receiving end. This paper followed the general principles of modeling in multipath effects, and the UHF band multipath effects of sea surface were studied. The judgment basis was obtained which determines whether the specula reflected wave dominates in the reflected wave based on Rayleigh criterion, and then the reflection coefficient of sea surface were calculated. Finally, the power attenuation of reflected wave relative to direct wave for different wind speeds were simulated and analyzed.

A Dual-Layer Broadband Compact UHF RFID Tag Antenna for Platform Tolerant Application

In this paper, we present a compact tag antenna for radio frequency identification (RFID) application. By embedding four parasitic planar inverted-F antennas under the top patch, four adjacent resonant modes are excited simultaneously and the impedance bandwidth is broadened to 140 MHz or more, which fully covers the entire worldwide ultra high frequency (UHF) band (860-960 MHz). The proposed antenna is printed on two FR4 substrates with a total volume of 56 mm×26 mm×3.2 mm. The measured read range was 4 m in a copper plate sized of 500 mm × 500 mm. Experimental studies demonstrate that the proposed antenna could work properly on general tagged objects.

Connector-less test setup for measurement of passive inter-modulation products at UHF band

This paper describes the establishment of a test setup for measurement of passive inter-modulation (PIM) products generated by various device(s) under test (DUT(s)) (filters, coaxial cables etc.) at ultra high frequency (UHF) band. The paper begins with a brief discussion of an ideal PIM test setup using a quiet load. It then discusses the establishment of the setup in the absence of quiet load and demonstrates a PIM level of −192 dBc of the test setup. Finally it shows the PIM performance of a band-stop filter, a flexible cable, cascade of band-stop filter, and flexible cable, measured using the established test setup. These components are required for UHF payload of a communication satellite.

UHF Wearable Rectenna on Textile Materials

A wearable rectenna for operation in the ultra high frequency (UHF) band is presented. The proposed device consists of a compact patch antenna and a full-wave bridge rectifier, both fabricated with textile materials. The patch antenna has been realized by using an adhesive conductive fabric on a bi-layer substrate made of pile and jeans. As for the rectifier, it is on a layer of jeans on the back-face of the antenna. Experimental data referring both to the patch antenna and to the rectenna are reported and discussed. From measurements performed with an incident power density of 14 μ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , it is demonstrated that the rectenna here presented exhibits a conversion efficiency higher than 20% over the frequency range 860-918 MHz with a maximum of about 50% at 876 MHz.

Spectrum occupancy investigation: Measurements in South Africa

Regulatory bodies have predicted an impending shortage in commercial radio frequency spectrum in the near future. However, due to outdated regulatory practices, many of these bands are in fact inefficiently underutilised. Spectrum measurement campaigns have be carried out around the world to determine the extent to which this is true. However, there still seems to be a lack of knowledge regarding spectrum occupancy in South Africa. A spectrum measurement system was thus designed and employed to measure the spectrum occupancy of the ultra-high frequency (UHF), global system for mobile communications (GSM) 900MHz and GSM 1800MHz bands through a measurement campaign in the Hatfield area of Pretoria, South Africa. A method for determining spectrum occupancy, from raw spectrum measurements, has been described and used to calculate the average spectrum occupancy of these bands. Occupancy in the UHF band was found to be fairly constant at approximately only 20%. While the maximum occupancy of the GSM 900MHz band was calculated to be much higher at approximately 92% and that of the GSM 1800 band to be approximately 40%. However, the GSM 900MHz and 1800MHz bands did exhibit fluctuations in occupancy of between 10% and 20% respectively according to the time of day. Slight variations in occupancy of between 1% and 3% were also evident over the days of the week. These results are placed into context by a comparison with the findings of various other measurement campaigns from around the world. When compared, occupancy was generally found to be lower in the UHF bands but higher in the mobile bands.

Graphene-based oscillator reaches the ultrahigh-frequency band

Graphene-based oscillator reaches the ultrahigh-frequency band

Multiband time‐of‐arrival positioning technique using an ultra‐high‐frequency bandwidth availability model for cognitive radio

In this study, the authors present a multiband time-of-arrival (TOA) positioning model and validate the performance in a practical dynamic spectrum access scenario according to results obtained from an ultra-high-frequency (UHF) spectrum occupancy measurement campaign. The statistical analysis of the measured data shows a distinguishable difference between the unoccupied and occupied portion of the UHF band. The bandwidth availability for the UHF band is shown to follow a Gaussian distribution according to the measurement results. The positioning model is verified using the non-linear least squares, linear least squares and two-step maximum-likelihood location estimation algorithms. The root-mean-square error (RMSE) performance evaluation of the proposed model revealed the advantage of utilising five discrete bands to perform TOA estimation, especially in poor signal-to-noise ratio (SNR) conditions ranging from – 10 to 0 dB. At a fixed SNR of 0 dB, an average RMSE improvement of 74 and 82% was observed for a double- and triple-band system when compared with a conventional single-band TOA system. This particular positioning technique can enable improved location estimation in a dynamic spectrum access environment.

E-WEHP: A Batteryless Embedded Sensor-Platform Wirelessly Powered From Ambient Digital-TV Signals

The use of digital television broadcasting standards has resulted in transmission of perpetually on wireless digital-TV signals over the air at wider bandwidths in ultrahigh-frequency bands for high-definition video and audio broadcasts to TV and smart phones. This paper presents a unique embedded wireless energy-harvesting prototype (E-WEHP) that exploits the unique makeup of ambient digital-TV signals, and scavenges wireless power from them at distance of over 6.3 km from the TV broadcast source. The harvested wireless power is successfully used to power and sustain a 16-bit embedded microcontroller for sensing and machine-to-machine applications without the use of batteries. The E-WEHP uses a miniaturized planar log-periodic antenna and RF-dc charge-pump circuit with maximum sensitivities of - 14.6 and -18.86 dBm and an embedded firmware-based power management scheme to power microcontroller peripherals from different types of ambient digital-TV signals.

Planar, Lightweight, Circularly Polarized Crossed Dipole Antenna for Handheld UHF RFID Reader

ABSTRACTA planar, lightweight, crossed dipole antenna with circularly polarized (CP) radiation is introduced for application in a radiofrequency identification handheld reader at ultrahigh frequency bands. The dipoles cross through a 90° phase‐delay line of a vacant‐quarter printed ring that enables broadband characteristic in terms of impedance matching and 3‐dB axial ratio (AR) bandwidths. Four printed inductors are symmetrically inserted into the dipole arms whose ends are barbed to achieve a compact size. A sample antenna with a size of 60 × 60 × 0.508 mm and weight of 3.6 g is designed, fabricated, and measured. The proposed antenna yields an impedance bandwidth of 851–941 MHz for |S11| &lt; −10 dB and a 3‐dB AR bandwidth of 902–921 MHz. At 910 MHz, the antenna radiates bidirectional CP waves with a gain of 1.4 dBic and an AR of 1.1 dB. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1874–1878, 2013

Novel electronic tuner using varactors for tunable RF front-ends

This paper presents a novel electronic tuner with high power handling capability utilizing varactors based on the asymmetric bilateral coupled microstrip transmission line. Through varying the bias voltage of the varactor at the Ultra High Frequency (UHF) band, the performance of the tuner is demonstrated according to simulated and measured results from several cases with the return loss (S11) below −20 dB and the insertion loss (S21) within ±0.5 dB. Compared with tuners using π and τ network, electronic tuner of this paper shows superior frequency agility as well as wide impendence coverage. Advanced biasing structure has been developed to improve power handling for high power level applications. It is expected that the novel tuner would be part of intelligent Radio Frequency (RF) front-ends system and cognitive wireless system in the future.

Ultrahigh-frequency surface electromagnetic waves in an open waveguide

An experiment in which guided propagation of surface electromagnetic waves (SEWs) on a free curved metal-dielectric interface was observed in the ultrahigh-frequency band (at frequencies of 850 and 1200 MHz) is described. The data on signal propagation over various paths and under various propagation conditions is presented. It has been found that the decrease of the wave field with increasing distance from the source follows the exponential law.

Network properties of mobile tactical scenarios

The mobile tactical network is a practical implementation of the mobile ad hoc network. Formed across tactical radios operating in the military very high frequency and low ultrahigh frequency bands, the mobile tactical network has distinctive characteristics when compared with generic mobile ad hoc networks, in particular with respect to its network topological behaviors and connectivity attributes. These characteristics must be understood and considered when selecting suitable network protocols. To this end, in this paper, a network science-based systematic modeling approach is applied to analyze typical deployment scenarios and identify fundamental tactical network properties. The novel framework employs realistic scenario models as well as radio physical layer performance parameters and channel models to effectively capture the dynamic network behavior that needs to be considered for protocol design. The results provide critical insights and guidance to the development of tactical network solutions. © Her Majesty the Queen in Right of Canada 2013

Measurement of UHF Signal Propagation Loss under Different Altitude in Hilly Environment

In this paper, the effect of environment and altitude on ultrahigh frequency (UHF) band has been studied. Both theoretical study and experimental investigations are conducted in order to model and characterize such complex communication medium. The experimental study is primarily aimed at critically analyzing the detrimental impact of channel condition on received power in hilly environment under different altitudes. The propagated signal strength varies from one place to another due to time varying channel condition as a result of obstacles between the transmitter and receiver. There is dramatic need to experimentally investigate such scenario in order to provide an avenue through which service providers can strategies their policies for effective wireless communication. Developing such channel models is extremely useful in communication systems design and simulation. The proposed model has been compared with ITU-R model for verification of the develop model for propagation loss prediction in hilly environment. The results obtained are compared with different measurement at various altitudes in hilly terrain environment.

A MINIMIZED WIDEBAND ANTENNA ARRAY WITH DECOUPLING NETWORKS FOR UHF RFID APPLICATIONS

A minimized wideband antenna array is presented for ultra-high frequency (UHF) radio frequency identiflcation (RFID) reader applications. The antenna array consists of two E-shaped patch antennas and a feeding network, with the overall size 200 £ 100 £ 20mm 3 . The feeding network could efiectively decrease the antenna mutual coupling and improve the bandwidth. The measured bandwidth is about 68MHz (896{964MHz) under the condition of voltage standing wave ratio (VSWR) less than 2, which covers various RFID bands including North American (902{928MHz), Chinese (920{ 925MHz) and Japanese (952{955MHz). The average gain is 4.5dBi in UHF band. The principles of the antenna and the feeding network are also discussed and analyzed in this paper. At last, the key parameters are studied and show the antenna robustness.

UHF Propagation Along a Cargo Hold on Board a Merchant Ship

The characterization of a Line of Sight (LOS) and a Non-Line of Sight (NLOS) link is performed over the military Ultra High Frequency (UHF) band (225 to 450 MHz). This is done using experimental results collected inside the cargo hold of a merchant ship. By analyzing the guiding effect associated with the cargo hold and its sub-structures, the channel characteristics of the environment can be determined. This important propagation mechanism is analyzed using the 3-D ray tracing simulator. Path loss for both topologies is studied and linear path loss models are proposed. Small-scale channel characteristics, such as the number of multipath components, decay factor of the multipath components and Root-Mean-Square (RMS) delay spread are studied and compared for the LOS and NLOS scenarios. Due to the guiding effect and multiple reflections along the cargo hold, both the LOS and NLOS scenarios are found to exhibit similar channel characteristics. A linear decay function is proposed to model the average Power Delay Profiles (PDPs). It is concluded that the linear model provides a good representation for the shape of the impulse responses for a cluttered environment with reflective substructures. This study is useful for the implementation of wireless sensor networks for status monitoring in maritime applications.

Omnidirectional Metamaterial Antennas Based on $\varepsilon$-Near-Zero Channel Matching

We present an analytical model and practical design tools to realize cylindrically-symmetric compact antennas based on the anomalous transmission properties of e -near-zero (ENZ) ultranarrow radial channels. The flexibility and exotic propagation properties in ENZ metamaterial channels are exploited here to tune and match cylindrically-symmetric antennas, without the need of complex external matching networks, in order to realize exciting antenna designs in terms of size, complexity and efficiency. We first model a homogenized Drude dispersive ENZ metamaterial channel to feed a radial parallel-plate waveguide; next we suggest a practical realization of this channel by using radial fins; eventually, we apply the obtained design formulas to realize single- and multi-band cylindrical antennas with a wide tunability range. The designed antennas may operate in the ultra-high frequency (UHF) band and may be realistically tuned over a large bandwidth. We envision applications in frequency-hopping, multi-band, compact, omnidirectional antennas.

Coherent radiation from extensive air showers in the ultrahigh frequency band

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the ultrahigh frequency band (300 MHz--3 GHz). The Fourier spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays at observation dominated by the curvature of the shower front. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ringlike region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna experiment, making the interpretation that they are due to ultrahigh energy cosmic ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection.

Design of an Ultra-Compact UHF Passive RFID Tag Antenna for a Medical Sample Tube

In this letter, a small-sized ultra-high frequency (UHF) RFID tag antenna for a medical sample tube is proposed. The RFID tag antenna is designed and fabricated based on the circular loop antenna used in the UHF band (Korea standard, 917 MHz to 923.5 MHz). The tag antenna size is reduced using a circular meander stub. The antenna has a physical size of 8 mm, which is about λ/40 in electrical length. The proposed tag antenna is molded into a medical sample and multitag identification is performed.

A Passive UHF-RFID System for the Localization of an Indoor Autonomous Vehicle

A global localization system combining odometry data with radio frequency identification (RFID) readings is proposed. RFID tags are placed at the ceiling of the environment and can be detected by a mobile robot unit traveling below them. The detection of the tags is the only information used in the proposed approach (no distance or bearing to the tag is considered available), but differently from similar localization setups reported in the literature, only a small number (about one each square meter or less) of tags are used. This is possible using a suitable tag's antenna in ultrahigh frequency band, expressly designed to obtain regular and stable RFID detection regions, which allows us to consider an efficient Kalman filtering approach to fuse RFID readings with the vehicle odometry data. A satisfactory performance is achieved, with an average position error of about 0.1 m. The hardware/software localization setup described in this paper is cheap and easy to use and may provide a satisfactory approach in several industrial and domestic scenarios.

Ungrounded composite right-/left-handed metamaterials: design, synthesis and applications

The design of ungrounded meander line inductors (UMIs) and ungrounded interdigital capacitors (UICs) employed in the practical realisation of a planar ungrounded composite right-/left-handed (UCRLH) metamaterial is presented. Accurate lumped-element circuit models are proposed based on partial element theory and conformal mapping method. New and accurate analytical design formulas, for both the UMI and the UIC at very high frequency and ultra high frequency bands are derived and successfully validated through a proper comparison with the existing measurement data and the results obtained with the full wave method of moments. Further insight is sought through the investigation of the resonance mechanism of a printed dipole antenna loaded with UCRLH metamaterial cells. A prototype of the loaded dipole is fabricated to confirm and validate the theoretical calculations. The experimental results are found to be in good agreement with the theoretical calculations.